Let me point out several sentences [with some added amplification] from the Glossary writeup on LGS that hopefully will help you and others to understand this better:

LGS and flora/fauna: A normal gut cannot keep the healthy germs from growing there. LGS is NOT "normal" and so long as it exists, most normal germs tend to pass right on through [dysbiosis, since the normal flora/fauna is missing]. Likewise, ALL parasitic conditions ONLY occur when the normal colonic ecology is destroyed (LGS [& dysbiosis]). Parasites [including Candida] are all around all of us every day. The reason we do not all have them is because our normal intestinal ecology is very unfriendly to them [a combination of other flora/fauna, surface gut conditions, presence/absence of sugar for fungus nutrients, etc. etc.].

Although it IS true that parasites [including Candida] will make any LGS worse by further damaging the intestinal wall, one has to have LGS first to be able to GET parasites.

LGS and Gas: LGS, all by itself, tends to promote fermentation instead of digestion. Fermentation produces
gas, and digestion does not. [this may be a separate effect, or it may contribute to the normal bacteria passing right thru rather than "sticking" around in the gut.]

First, the bacterial ecology in the gut is a very delicate (though normally stable) one. It is made up of about 500 different species. LGS is a big strain on that delicate balance AND as soon as it begins to change (dysbiosis) the thousands of pathogenic beasties out there are quick to exploit that opening. Once THEY are established, THEY tend to displace the good bacteria left mainly because the very things that caused the LGS in the meantime are still operating.